You definitely have this backwards.  Used prices will potentially go up by the tax credit amount. The $35k effective price for a new one is the maximum/ceiling value of a used one, but after the tax credit goes away the new maximum value increases to the $43k. 

You have things backwards, you mean second hand prices would go up? Think about it logically, let us say a car costs 40k. You get 7.5k tax credit on new one. Would you pay even 33k for a 1 year used one? Being eligible for the tax credit hurts your resale value the same as it costs to buy. This is why Tesla Model 3 resale value dropped in the past 6 month in the first place, because of the tax credit as Tesla was not eligible for it and now became eligible